What is happening
You arrive at a classroom measuring a bench when the metre rule has gone missing.
The bench has to be logged before the new tables arrive and there is no rule in the room. One handspan measures 15 cm, and the bench runs 180 cm.
Measuring without a rulerRunning
Length measured
270cm
Bench length
180cm
Length measured is over by 90 cm
Number line. Handspans counted at 18 spans. Length measured 270 cm, Bench length 180 cm. Currently length measured is over by 90 cm.
What has to balance